Medicine is, more often than we care to admit, a series of lucky breaks, persistence, drawbacks, horrible personality clashes and, very occasionally, miraculous events. The story of how penicillin came to be discovered fulfils all these criteria and more.

It is quite easy to forget that 60 years ago, every hospital in Britain had its 'septic' ward, where patients who had picked up nasty bacterial infections came and, more often than not, died. Bandages and rest were about the best they could expect, for no one had developed a powerful antibiotic which would work in a living human being by killing the germs.

The discovery of penicillin, which was developed in the middle of the Second World War, is one of the most remarkable medical dramas, and any number of mishaps would have delayed its discovery. In this searching story, Eric Lax goes into enormous detail about its history and the subsequent squabbles over who really made the breakthrough. It is not a light read and some chapters become bogged down in personal histories of the characters, but the twists and turns of the research are fascinating.

It was, of course, Alexander Fleming who first discovered penicillin in his laboratory at St Mary's Hospital in Paddington, west London, in 1928. He noticed that when mould was growing in a Petri dish, there seemed to be a ring of clear liquid around it. What he was actually looking at was the ring of dead, transparent cells which lay between the mound of mould on a sea of staphylococci bacteria.

Fleming, a shy man, was intrigued by what he saw but could not find a way of extracting enough of it from a soupy broth to be able to inject it into anyone. The juice was too impure to be of any therapeutic use.

It was an Australian, Howard Florey, who realised its potential a decade later. He recruited the right people to work with him at Oxford University's School of Pathology, and Lax rightly gives credit to some of the hitherto forgotten characters, such as Norman Heatley, the man who found a way, using some Heath Robinsonesque devices, of extracting the penicillin from this chemical broth without making it ineffective.

There was also Ernst Chain, the biochemist who was researching antibacterial agents. Early in 1938, Chain came across one of Fleming's papers and wondered how it was that penicillin might be inhibiting the growth of bacteria. What we know now is that penicillin breaks down the cell walls of bacteria, dissolving them to render them useless. Chain quickly started some experiments and realised it was a fairly unstable and 'difficult' chemical. That only made him more interested.

It seems to have taken at least a year before Florey became really interested in it, although this is the subject of academic dispute. But the professor saw its potential as a substance which might actually work in vivo.

Efforts to develop it were made even harder by the outbreak of war. Luckily, the War Office decided to help Florey with funding, as long as he spent one-third of his time on poison gas research.

Incredibly, the staff in the unit would spend their mornings filling sandbags as protection against air raids, while trying to do research in the afternoons. In May 1940, the key moment came when they had to test the safety and its effectiveness of penicillin on mice which had been given a small dose of virulent streptococci, dangerous and common bacteria. Hour by hour, they watched to see the mice which were given a penicillin injection gradually recuperate while the others died.

Even though they were using a very impure form of penicillin, Florey and his team realised the importance of what they had achieved.

The following day, 350,000 men were rescued from Dunkirk because of the advancing Nazi threat. The title of the book refers to the fact that the scientists injected the antibiotic into their garments. If the Germans had invaded, they would have had to destroy the chemical but it would have survived unharmed in their clothes, safe for future research.

Ever greater quantities of penicillin were needed for more tests on mice, and Heatley had to borrow biscuit tins from various groceries around Oxford to keep it in. In fact, they ended up using many containers - petrol cans, pie dishes and old baths.

They then faced the problem of how to develop the drug. At that stage, they could make only very small quantities of it and it was hard to organise any trial involving patients. That meant the team could not get backing from a drugs company.

The first person to receive penicillin was Pc Albert Alexander who had been infected while working on his roses. 'The bacteria were eating him like a a worm in an apple,' writes Lax. Within days, Alexander's condition stabilised. But the drug ran out and the doctors and researchers had to stand by helplessly while he died.

Eventually, however, enough was produced with American help for many soldiers' lives to be saved by the drug.

In 1945, Chain, Florey and Fleming were jointly awarded the Nobel Prize for Physiology and Medicine for discovering penicillin and its curative action. Only three names could be attached to the prize and there was no mention of Heatley. He even turned down a share in the royalties from the development of another drug, cephalosporin, and died without the glory, fame or money. Eric Lax has now righted that injustice.